In the canning and bottling industries it is common practice to insert a small quantity of liquid nitrogen into the cans or bottles immediately prior to closure. The liquid nitrogen vaporizes in the can or bottle and displaces air from the can or bottle before the closure is applied.
When filling cylindrical cans of uniform diameter it is quite convenient to dispense liquid nitrogen in a continuous spray since the percentage of liquid nitrogen wasted is relatively small. However, this technique is extremely wasteful for bottles having relatively small necks, for example beer bottles.
In order to introduce liquid nitrogen into beer bottles it has been proposed to drop a discrete quantity of liquid nitrogen into each beer bottle immediately prior to closure. However, apparatus for effecting this process has not worked particularly successfully. In particular, instead of discrete slugs or droplets of liquid nitrogen descending into the bottles from a dispenser the bottles have been assailed by a diverging cone of minute droplets only a tiny portion of which enter the bottle. This problem has been variously attributed to:
(1) the liquid nitrogen (boiling point -196.degree. C.) starting to vaporize in the dispenser tube, i.e., the tube between a vacuum insulated vessel containing the cryogenic liquid and the atmosphere; and
(2) ice forming and partially blocking the outlet of the dispenser tube.
In order to compensate for the former problem the prior art has attempted to keep the dispenser tube as cold as possible (see UK 2 092 552A). Whilst such attempts marginally improved the situation the problem was still apparent particularly on high speed bottling lines. Furthermore, the additional cooling aggravated the existing problem of ice and frost build up on and obstructing the outlet of the dispenser tube.
In order to overcome the second problem it has been proposed to provide a blanket of cold gaseous nitrogen circumjacent the dispenser tube (see FIG. 1 of UK 2 169 998A).